LED car lights flicker - no need!

Surely they can design LED lights on cars to have a higher frequency PWM? Even £100K cars flicker dramatically, especially when filmed. It makes them look really cheap. All it would take is a higher frequency PWM, or a smoothing capacitor?

--
In 2005 eight Brits (All Scottish) cracked their skulls while throwing up into the toilet.

On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency
PWM= ? Even =A3100K cars flicker dramatically, especially when filmed.
It m= akes them look really cheap. All it would take is a higher
frequency PW= M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just
as well use DC direct from the battery. I don't know the technical
reasons why but apparently using the equivalent DC voltage required to
get the same brightness as you can get by strobing them would burn them
out. I'm sure some electronics guru on here can explain more. But it
does lead to interesting effects on video as you say )

Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order. Seeing a flicker
from them on a video is the same effect as wagon wheels appearing to turn
backwards on old cowboy and indian films - stroboscopic effect.

--
*WHY IS THERE AN EXPIRATION DATE ON SOUR CREAM?

Dave Plowman dave_at_davesound.co.uk London SW 12

DavidRGuest

Tue Apr 23, 2013 10:36 am

<neil_at_the.shed> wrote in message news:kl5ibr$qiu$1_at_speranza.aioe.org...

Quote:

On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency PWM=
? Even =A3100K cars flicker dramatically, especially when filmed. It m=
akes them look really cheap. All it would take is a higher frequency PW=
M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery. I don't know the technical reasons
why but

The effect relies on the persistance of the eyes to make it appear that the
average brightness is higher. Smoothing at source would be less energy
efficient.

Agreed the effect is not pleasant. It would help if they could introduce
softer start for indicators and brake light dimming when conditions suggest
a slow moving queue.

Surely they can design LED lights on cars to have a higher frequency PWM=
? Even =A3100K cars flicker dramatically, especially when filmed. It m=
akes them look really cheap. All it would take is a higher frequency PW=
M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery. I don't know the technical reasons why but
apparently using the equivalent DC voltage required to get the same brightness
as you can get by strobing them would burn them out. I'm sure some electronics
guru on here can explain more. But it does lead to interesting effects on
video as you say )

Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order. Seeing a flicker

Its odd though isn't it. The way they're constructed must mean the amount of
heat generated for a given voltage or current must slowly tail off so although
they'd heat up too much at constant voltage X you can pulse them at for
arguments sake X*2 producing the same or even more total light but without a
doubling of the heat generated so allowing for cooling down to safe levels
during the OFF periods of the pulse. Or something like that.

In article <kl5ibr$qiu$1_at_speranza.aioe.org>,
neil_at_the.shed> wrote:
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency
PWM= ? Even =A3100K cars flicker dramatically, especially when filmed.
It m= akes them look really cheap. All it would take is a higher
frequency PW= M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just
as well use DC direct from the battery. I don't know the technical
reasons why but apparently using the equivalent DC voltage required to
get the same brightness as you can get by strobing them would burn them
out. I'm sure some electronics guru on here can explain more. But it
does lead to interesting effects on video as you say )

Pulsing an LED is a way of getting a higher light output from it without
overheating. Overheating an LED kills it in short order.

Take for example the brake/tail lights. These are often pulsed for tail and on for brake. So what you said doesn't make sense. Anything less than full voltage on (as for brake) will be lower heat.

Quote:

Seeing a flicker
from them on a video is the same effect as wagon wheels appearing to turn
backwards on old cowboy and indian films - stroboscopic effect.

It's way worse than that - the duty cycle is quite a lot less than 50%, so you see them off, with the occasional on.

neil_at_the.shed> wrote in message news:kl5ibr$qiu$1_at_speranza.aioe.org....
On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency PWM>>> ? Even =A3100K cars flicker dramatically, especially when filmed. It m>>> akes them look really cheap. All it would take is a higher frequency PW>>> M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery. I don't know the technical reasons
why but

The effect relies on the persistance of the eyes to make it appear that the
average brightness is higher.

Easy enough to double the frequency of the flicker, then you wouldn't notice it. Remember 50Hz CRT monitors?

Quote:

Smoothing at source would be less energy efficient.

I don't believe you. Switched mode power supplies are very cheap nowadays, especially compared with the cost of a car, especially a £100K car which has the same problem.

You can get a very smooth DC voltage of any level out of one - just look at your PC power supply then think of a smaller version of it. There are in fact smaller versions of it on your motherboard changing 12 volts to the CPU voltage (which is in fact variable).

Quote:

Agreed the effect is not pleasant. It would help if they could introduce
softer start for indicators

I prefer them to go on and off suddenly. The only problem I have is flickery tail lights.

Quote:

and brake light dimming when conditions suggest a slow moving queue.

I don't agree with different brightnesses of brakes. We already have two brightnesses of red - tail and brake. Adding more would just lead to confusion, you would wonder if it was a tail or a brake.

--
"It is generally inadvisable to eject directly over the area you just bombed." - U.S. Air Force Pilot training manual

Major ScottGuest

Tue Apr 23, 2013 2:40 pm

On Tue, 23 Apr 2013 09:56:27 +0100, <neil_at_the.shed> wrote:

Quote:

On Mon, 22 Apr 2013 19:44:38 +0100
"Major Scott" <no_at_spam.com> wrote:
Surely they can design LED lights on cars to have a higher frequency PWM=
? Even =A3100K cars flicker dramatically, especially when filmed. It m=
akes them look really cheap. All it would take is a higher frequency PW=
M, or a smoothing capacitor?

They flicker for a reason. If they smoothed the current they might just as
well use DC direct from the battery.

No, provide them with a lower DC voltage to make them dimmer. Say 12V for brake and 9V for tail.

Quote:

I don't know the technical reasons why but
apparently using the equivalent DC voltage required to get the same brightness
as you can get by strobing them would burn them out. I'm sure some electronics
guru on here can explain more. But it does lead to interesting effects on
video as you say )

So you're saying that on brake they are also strobed? I have never noticed a brake strobing. It's the tails that do it.

In article <op.wvzz3ywg2eh2io_at_red.lan>,
Major Scott <no_at_spam.com> wrote:
Pulsing an LED is a way of getting a higher light output from it
without overheating. Overheating an LED kills it in short order.

Take for example the brake/tail lights. These are often pulsed for tail
and on for brake. So what you said doesn't make sense. Anything less
than full voltage on (as for brake) will be lower heat.

LEDs are current, not voltage, driven.

When there's a series resistor, then you can think of them as voltage driven. Anyway electronics to lower the current can be made without pulsing.

--
When shagging a goat you are best taking it to the edge of a cliff because they push back harder. -- Billy Connelly